Kevin is 4 times as old as Tiffany and is also 30 years older than Tiffany. How old is Tiffany?
Solution: We can use the given information to write down two equations that describe the ages of Kevin and Tiffany. Let Kevin's current age be $k$ and Tiffany's current age be $t$ $k = 4t$ $k = t + 30$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $t$ , and both of our equations have $k$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4t$ $-$ $ (t + 30)$ which combines the information about $t$ from both of our original equations. Solving for $t$ , we get: $3 t = 30$ $t = 10$.